Ground water drawn from intermediate aquifers of various parts of West Bengal and Bangladesh was found to contain arsenic above the permissible limit of 0.05 ppm. The WHO recommended limit being 0.01 ppm. Thus the water from tube wells and hand pumps is unsuitable for drinking purpose. Arsenic contamination of ground water therefore assumed a serious public health issue as ground water serves more than 80% of the drinking water needs primarily in the rural sector.
Various physical and chemical processes are known for removing arsenic from wastewater for recovery and/or as a pollution abatement measure. Separation can be achieved by arsenic adsorption on amorphous aluminum hydroxide. By such means, as discussed in the Journal of Colloids and Interface Science, volume 54, No. 3, pages 391-399, 1976, a plateau of 0.3 ppm arsenic can be attained but further reduction of arsenic content is difficult.
It is also known that by precipitation with calcium oxide and ferric chloride the arsenic concentration in waste water has been reduced from 1000 ppm to 5 ppm as described by J. Hollo et al in Polytech. Chem. Engg. (Budapest)12(3); page 283-292, 1968.
Japanese Patent 20952 (1974) described the use of both slaked lime and bleaching solution together with magnesium chloride for removal of Arsenic(III) from waste water wherein a waste water containing 2490 ppm Arsenic(III) was stirred with these reagents and upon filtering the precipitates, the filtrate had a arsenic content of 3.07 ppm.
The U.S. Pat. No. 4,201,667 (1987) describes a process for removing arsenic from aqueous mediums wherein sufficient calcium hydroxide is added in the presence of phosphorous to adjust the pH of the aqueous medium from about 7.0 to 11.5 whereby precipitates of both arsenic and phosphorous are formed and subsequently separated from the aqueous medium. In this process the stirring time was reported to about 30 minutes and separation of the precipitate may be achieved by filtration, settling and decanting, and settling followed by filtration of the supernatant. The arsenic content in the treated water was above 0.01 ppm using this technique.
References is also made to publications by Prasun Bhattacharyya et al and S. Bhattacharyya et al in the Proceedings of International workshop on “Control of arsenic contamination in ground water” held on Jan. 5-6, 2000 published by PHED, Govt. of West Bengal, wherein laterite was used as an adsorbent for treatment of arsenic contaminated water. In the above noted proceedings, Prasun Bhattacharyya et al reported that the efficiency varied between 50-90% for 5 gm of added laterite per 100 ml water under an equilibration period of 20 minutes and S. Bhattacharyya et al reported that 0.2 gm laterite ore can absorb 67.4% and 61.3% arsenic from 100 ml of 0.27 ppm As(III) or 0.182 ppm of As(V) solution and a shaking time of 5 minutes is found to be optimum for 0.4 gm laterite ore and 100 ml solution of aforesaid concentrations of Arsenic (III or V).
References is also made to the publication of Environmental Systems Information Center, Asian Institute of Technology, March, 1996 on “Drinking water without arsenic: a review of treatment technology”, by T. Viraraghavan. K. S. Subramanian and T. V. Swaminathan wherein the advantages and disadvantages of various technology options were described. The conventional techniques for treatment of arsenic contaminated water are primarily based on chemical treatment or co-precipitation technique and adsorption technique which have been tested under field conditions using ground water containing arsenic in the range of 0.1-1 ppm level and arsenic level in the treated water was found to be above WHO recommended limit of 0.01 ppm of arsenic content in drinking water. The co-precipitation technique suffers from the disadvantages like controlling the dose of chemicals, ineffective mixing of chemicals and contaminated water, slower settling rate of the fine particles of precipitating materials, inefficient filtration of fine particles by slow or rapid sand filter due to which the efficiency of arsenic removal is lower particularly in the higher concentration range of arsenic [above 0.5 ppm] in the contaminated water and the arsenic content after treatment is higher than the WHO recommended limit of 0.01 ppm of arsenic in drinking water. The drawbacks of the activated alumina adsorption technique are insufficient contact time, coating of alumina grains by fine particles of iron present in raw water thereby reducing the efficiency of adsorption and necessity of frequent back washing, shifting the problem of water pollution to soil contamination which is of more serious concern to environmental pollution particularly in the vicinity of treatment plant.
Existing arsenic removal methods and equipments revealed that there is a definite need for improvement in producing safe drinking water as per recommendation of WHO.
It is known to use porous ceramics for separation of suspended particulate matter present in liquid and gaseous streams by passing the same through the porous ceramic tubes and plates for pressure filtration application. Another important use of such porous ceramic material are for preparation of ceramic membranes consisting of a coating of finer particles over the porous ceramic matrix to form a composite structure of graded pore size which are primarily used for micro, ultra and nano filtration application.
Reference may be made to U.S. Pat. No. 126,508 wherein the raw materials used for the preparation of porous ceramic candles were coarser and angular grains of silica and a naturally occurring clay having much impurities causing wide pore size distribution, poor strength and formation of glassy matrix unsuitable for cleaning by strong alkalis and high pressure steam. The drawback of conventional porous ceramic candle filters are    1. Larger pore size varying in the range of 5-30 μm.    2. Owing to such broad pore size distribution, the efficiency of separation is much less and the chances of the pores clogging are very high due to penetration of the finer suspended particulates posing problems of frequent cleaning.    3. The suspended particles of relatively lower sizes passes through higher pore size of the porous candle when the filtration takes place under atmospheric pressure.
To overcome this problem, cartridges of polymeric materials have been developed which has an integral skin of finer pore sizes as described in the reference Porter, M. C., 1990, Handbook of Industrial Membrane Technology, Noyes Publication, Park Ridge, N.J. However, such materials also suffer from limitations of                1) poor chemical stability        2) low abrasiveness        3) low durability towards microbial attack,        
Ceramic materials have several key performance advantages over their polymeric counterpart due to which porous ceramics are gaining considerable importance and industrial applications. Reference may be made to the paper “The control of pore size in the manufacture of ceramic filters”, R. A. Clark, M. F. Hall and J. W. Kirk, in the British Ceramic Proceeding, No. 43, December 1988, Institute of Ceramics, U.K. wherein the technique adopted for the manufacture of ceramic filters utilizes differently sized irregularly shaped non-plastic alumina particles following the theories of particle packing of different grain size range to control porosity and pore size in the filter. The drawbacks of this process are use of costly raw materials, difficulties in fabrication of the non-plastic component by slip casting, use of costly equipment like extruder and necessity of firing at high temperature above 1550° C. resulting in higher cost of filters.